1. Field of the Invention
The present invention relates to an image sensor with signal processing system, and more particularly to an image sensor with sampling control system. Such an image sensor with sampling control system may be advantageously applied to a field of developing a robot vision system as well as a field of image measurement.
2. Description of the Related Art
In general, in an image processing system an image is picked-up by an image acquisition device such as a CCD camera to derive an analog image signal, and after converting the analog image signal into a digital image signal by an analog-digital converter, the thus converted digital image signal is supplied to a digital image processing device. In order to increase an image processing speed, these devices have been designed to have high operating speed. However, since the image signal outputted from the image acquisition device is a serial signal, the overall processing speed is limited. In HDTV, a high speed operation is realized by deriving the image signal by means of two pixel read-out lines.
On the other hand, in accordance with a progress in VLSI technology, it has become possible to arrange various peripheral circuits around an image sensing unit on a single semiconductor chip. There have been proposed image sensors with various image processing systems. Such image sensor is called a computational image sensor or smart image sensor, in which an image sensing section and an image processing section are formed on a same semiconductor chip.
Heretofore, there have been proposed an image sensor with random access system, an image sensor with skip access system, an image sensor with block address system and a polar coordinate type image sensor.
FIG. 1 is a block diagram showing a known typical image sensor with random access system. This image sensor includes an imaging cell array 51, a row decoder 52, a column decoder 53, a column selector 54 and an output section 55, all of these components being formed on a single semiconductor chip. In this known image sensor, coordinates of pixels within a given block on the imaging cell array 51 are denoted from an external with a unit of row and column. That is to say, an input value r from the row decoder 52 and an input value c from the column decoder 53 are converted into coordinates, and a pixel value of the denoted coordinates is selectively read-out. In this known image sensor, respective pixels of the imaging cell array 51 have to be accessed, and thus address information is always required for performing the random access.
Also in the known image sensor with block access control system as well as in the known image sensor with skip access control system, the read-out of the image signal is performed principally in accordance with the access with a unit of row and column. Therefore, by inputting row and column addresses, a pixel value of a pixel at denoted row and column can be deleted or selected, and an image signal can be selectively read out of a desired block on the imaging cell array. Furthermore, by performing a sub-sampling for pixel array, a size of an output image can be reduced. However, in these image sensors, pixel values could not be read out of a smaller area than the block denoted by the row and column information.
In the polar coordinate type image sensor, a central portion and a peripheral portion of the image sensing section are formed by imaging cell arrays arranged with different density. That is to say, the central portion is composed of pixels arranged with a higher density and the peripheral portion is composed of roughly arranged pixels. Therefore, it is possible to attain a higher resolution in the central portion than the peripheral portion. In this manner, the polar coordinate type image sensor can resemble a fovea of a human eye. However, since the central and peripheral portions are constructed fixedly, upon unifying this image sensor with a vision system, the image sensor has to be always moved in accordance with a movement of a focus. Furthermore, this image sensor could be used only to an application resembling a fovea of a human eye, and therefore a range of application is limited.
In the above mentioned image sensor with random access system, an image signal can be read out of an arbitrarily selected or denoted pixel or pixels, but this control requires always pixel address information, and thus high speed access could not be realized.
In the image sensor with skip address system as well as in the image sensor with block access system, an image signal can be read out of any desired block denoted on the imaging cell array, but an image signal could not be read out of an area smaller than the block denoted by the row and column information. For instance, a single pixel could be not be selectively read out.
In the polar coordinate type image sensor, since the pixels are arranged in accordance with a fixed pattern resembling a fovea of a human eye, the application is limited.
The present invention has for its object to provide a novel and useful image sensor with sampling control system, in which access to respective pixels as well as pixels within any desired block can be performed without requiring address information, a control of image resolution can be performed with a pixel unit, and a high speed access can be attained.
It is another object of the invention to provide an image sensor with sampling control system, in which a sampling corresponding a fovea of a human eye can be performed while a focus movement within an image pick-up plane is not required when the image sensor is unified with a vision system, and a versatile sampling can be carried out without being limited to a fovea of a human eye.
According to the invention, an image sensor with sampling control system comprises:
a sensor unit having a number of pixel circuits arranged in matrix;
a memory unit having a number of memory circuits arranged in matrix, the number of said memory circuits being equal to that of said pixel circuits, a first horizontal shift register for writing memory values constituting a pixel read-out pattern into said memory circuits in accordance with a sample selection signal;
a first vertical shift register for generating a signal for writing said memory values into said memory circuits as well as a signal for reading said memory values out of said memory circuits;
a second vertical shift register driven in synchronism with said first vertical shift register to generate a signal for reading out pixel values from said pixel circuits as well as a reset signal to said pixels circuits;
a second horizontal shift register for outputting pixel value or values selected in accordance with the memory values stored in said memory circuits;
a third horizontal shift register for outputting all pixel values; and
a switch unit for controlling of read-out of the pixel values from any one of said second and third horizontal shift registers in accordance with the memory values stored in the memory circuits.
In the image sensor with sampling control system according to the invention, all the above mentioned components may be formed on a single semiconductor chip. Furthermore, by suitably selecting said memory values denoting the pixel read-out pattern, any desired sampling can be performed at a high operating speed.
In a preferable embodiment of the image sensor with sampling control system according to the invention, each of said memory circuits of the memory unit includes three NMOS switches, an electrical energy storing element and an inverter.